The “American Pie” franchise shows some unflattering wrinkles with “American Reunion,” a mediocre and all-too obvious sequel that utterly fails to recapture the youthful spark of its original.

And what a disappointment that is. The 1999 gut-buster remains one of our funniest raunchy comedies, and its antics remain seared into our collective pop-culture consciousness. Who can forget the seemingly virtuous Michelle (Alyson Hannigan) recounting her exploits in “band camp” or Jim (Jason Biggs) and his encounter with a warm apple pie?

Nothing in “Reunion” — which gathers original cast mates now as early thirtysomethings for this installment — remotely approaches those wild high jinks.

“Reunion’s” failure could be attributed to its own success. “Pie,” which was followed by two sequels — “American Pie 2” and “American Wedding” — could be partially credited for paving the way for edgy, go-for-broke recent fare such as “The Hangover,” “Bridesmaids,” even “21 Jump Street.” But compared to those belles of the comic ball, “American Reunion” is simply a wallflower.

Directors and screenwriters Jon Hurwitz and Hayden Schlossberg (creators of “Harold and Kumar”) tease out a few chortles, but they’re sporadic and don’t have much zing. In fact, one of the biggest laughs comes at the film’s end — so don’t dash out of the theaters, assuming you make it that far.

The biggest disappointment is the lack of oh-my-God-are-they-really-going-to-do-that comedic shockers, which are pretty much the hallmark of this series. We get a full-on gander at scrunched-up male genitals, but it’s silly, not outright hilarious.

Gross-out humor gets sprinkled in here and there, yet it all seems stale, juvenile and much too icky. Even the reunion scenario fails to live up to expectations, with the actual event generating muted laughter at best, while clumsily wrapping up all the relationship melodrama.

The actors give it their all, but the characters, like the film itself, remain stuck in a 1999 rut.

Jim is still pleasuring himself, but he is now fending off the ludicrous advances of an 18-year-old he used to baby-sit while trying to mend a sexless marriage to Michelle. Stifler (Seann William Scott) remains the sociopath, resorting to dumb and dumber tricks to avoid being an adult. “Oz” (Chris Klein — good to have you back) is a sportscaster and former reality TV contestant involved with a vapid model (Katrina Bowden), but still toying with an old flame, Heather (Mena Suvari).

None of the problems these characters encounter is nearly as interesting as what the parents are up to. Eugene Levy, as Jim’s nerdy dad, and Jennifer Coolidge, as Stifler’s sexpot mom, show the kids up, with Levy tapping into some tender emotions as a still grieving husband.

But they’re only side notes in a sequel that seems an awful lot like an Adam Sandler comedy.

“American Reunion” isn’t nearly as bad, but that’s not much of a compliment. After three films, “Reunion” should have graduated up to bigger and better things.